Device for measuring the mass of a flowing medium in an intake tube

ABSTRACT

A device for measuring the mass of a flowing medium with a temperature-dependent measurement element has a measurement conduit whose faces, which extend perpendicular to a surface fixed by the measurement element, are inclined and approach each other in the flow direction of the medium in the measurement conduit. The invention is provided for measuring the mass of a flowing medium to measure the intake air mass of internal combustion engines.

PRIOR ART

The invention is based on a device for measuring the mass of a flowingmedium. A device has already been disclosed (DE-PS 44 07 209), which hasa temperature-dependent measurement element that is accommodated in ameasurement conduit that extends in a straight line. The measurementconduit extends in the device from an inlet to an outlet, which isadjoined by an S-shaped deflection conduit. The flowing medium flowsfrom outside into the measurement conduit and then into the deflectionconduit, where it flows out again from an outlet opening. Themeasurement conduit has a rectangular flow cross section, wherein twoside faces oriented toward the platelet-shaped measurement element areembodied extending obliquely so that a tapering of the measurementconduit is produced in the flow direction of the medium in themeasurement conduit. A top face of the measurement conduit, whichextends lateral to the side faces and from which the measurement elementprotrudes, and a bottom face of the measurement conduit disposedopposite this top face thereby extend in a level or parallel fashion,with a constant distance from each other.

A device equipped with such a measurement conduit is also known from theSAE Paper 950433 (International Congress and Exposition Detroit, Mich.,Feb. 27-Mar. 2, 1995, can be inferred from the sectional depiction inthe top picture in FIG. 7 on page 108, the measurement conduit and thedeflection conduit are essentially comprised of two parts, wherein apart referred to below as the base part, with the measurement element,includes a side face, a top face, and a bottom face of the measurementconduit and the deflection conduit. The other part has only the secondside face of the measurement conduit and the deflection conduit and thusconstitutes a cover part. The base part and the cover part arepreferably made of plastic, for example using the plastic injectionmolding technique. Because of the tapering shape of the side fades ofthe measurement conduit, an increasing wall thickness is produced in theflow direction. In the manufacturing, it has turned out that due to theincreasing wall thickness, varying cooling speeds and accumulations ofmaterial occur, which can in particular lead to hollows in the sidefaces of the measurement conduit. In a provided mass production of thedevice, this results in more or less intense variations in theachievable measurement precision of the devices.

ADVANTAGES OF THE INVENTION

The device according to the invention for measuring the mass of aflowing medium has the advantage over the prior art that in massproduction, devices with a properly manufactured housing can be producedso that only extremely slight variations in the measurement precisionoccur. It is also particularly advantageous that by means of theembodiment, according to the invention, of the walls of the measurementconduit, an acceleration of the flow in the measurement conduit canfurthermore be maintained, which leads in a known manner to astabilization of the flow of the medium in the measurement conduit,particularly at the inlet.

Advantageous improvements and updates of the device disclosed arepossible by means of the measures taken.

An inclined embodiment of an edge face of the deflection it conduit isparticularly advantageous, with which it is possible to further simplifythe manufacturing of the measurement conduit and the deflection conduit,wherein a further improvement of the measurement result also occurs.

Furthermore, a flow connection to the external flow in the intake lineis provided in the deflection conduit in the form of an opening, bymeans of which possibly existing residual interferences of a pressurewave in the deflection conduit can be completely eliminated so that afurther improvement of the measurement result can be achieved.Furthermore, the device has a considerably reduced measurement signalnoise, which can be produced by means of turbulences that occur in themeasurement conduit.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are shown in simplified form inthe drawings and will be explained in more detail in the descriptionthat follows.

FIG. 1, in a partially sectional depiction, shows a side view of thedevice according to a first exemplary embodiment according to theinvention,

FIG. 2 is a section through the device along a line II—II in FIG. 1,

FIG. 3, in a partially sectional depiction, shows a side view of thedevice according to a second exemplary embodiment according to theinvention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

In a partially sectional depiction, FIG. 1 shows a side view of a devicelabeled 1, which is used to measure the mass of a flowing medium, inparticular the intake air mass of internal combustion engines. Theinternal combustion engine can be a mixture compressing engine withexternally supplied ignition, or it can also be an air compressing,self-igniting engine. The device 1 has, for example, a narrow, rod-like,block-shaped form that extends longitudinally in the electricaldirection of the plug axis 10, and is inserted into an opening let intoa wall 8 of an intake line 9, for example 90 that it can be plugged in.The device 1 is sealed by means of a sealing ring 3 to an outsideelectrical source in the wall 8, and is connected to the wall, forexample by means of a screw connection that is not shown in detail. Thecross-hatched wall 8 is part of the intake line 9 that is embodied forexample as cylindrical, through which the internal combustion engine canaspirate air from the environment by way of an air filter that is notshown in detail. The wall 8 of the intake line 9 defines a flow crosssection that in the case of the cylindrical intake line 9, for example,has a circular cross section in the center of which a center axis 11extends in the axial direction, parallel to the wall 8, and this axis isoriented perpendicular to the plug axis 10. With a part referred tobelow as the measurement part 17, the device 1 protrudes into theflowing medium, wherein the measurement part 17 is disposed, forexample, approximately in the vicinity of the center of the intake line9.

The device 1 is composed, for example, in one piece out of themeasurement part 17, a support part 18, and a securing part 19, and ispreferably made of plastic using the plastic injection moldingtechnique. A measurement element 21 is embodied for example in the formof a so-called micromechanical component and has a plate-shaped,silicon-based support body 20 with an etched-out, membrane-shaped sensorregion with an extremely slight thickness and a number of likewiseetched-out resistive films. These resistive films constitute at leastone temperature-dependent measurement resistor and for example oneheating resistor. Preferably, the heating resistor is disposed in thecenter of the membrane and, with the aid of a temperature sensor, isregulated to an over temperature. Upstream and downstream of the heatingregion constituted by the heating resistor, two measurement resistorsare disposed symmetrically to the heating region. A measurement elementof this kind is known from the SAE Paper 950433 mentioned above, as wellas from DE-OS 42 19 454, and U.S. Pat. No. 5,404,753, the disclosure ofwhich is expressly intended to be a component of the current patentapplication. The support body 20 of the measurement element 21 isaccommodated flush in a recess in a plate-shaped mount comprised, forexample, of metal, and is secured there, for example, by means ofadhesive. The individual resistive films of the measurement element 21are electrically connected by means of connecting lines 26 that extendinside the device 1 to an electronic evaluation circuit 27 depicted withdashed lines in FIGS. 1 and 3, which includes, for example, abridge-like resistive measurement circuit. With a plug connection 28provided on the securing part 19, the electrical signals produced by theevaluation circuit 27 can also be supplied, for example, to anotherelectronic control device for evaluation.

As depicted in FIGS. 1 and 2, the measurement part 17 of the device 1has a block-shaped form and a measurement conduit 30 that extends alonga measurement conduit axis 12 that extends centrally in the measurementconduit 30 from an inlet 32 with a rectangular cross section to anoutlet 33 that likewise has a rectangular cross section. The device 1 isinstalled in the intake line 9, preferably with the measurement conduitaxis 12 parallel to the center axis 11. However, it is also possible toinstall the device 1 with an oblique installation position, rotatedaround the plug axis 10. In addition to or instead of the obliqueinstallation position, it is also conceivable to install the device 1 ina tilted installation position, inclined around the center axis 11. Themeasurement conduit 30 transitions downstream into an S-shapeddeflection conduit 31. The measurement conduit 30 is defined by a topface 37, which is farther from the center axis 11 and is disposed abovein FIGS. 1 and 3, and by a bottom face 38, which is closer to the centeraxis 11 and is disposed below in FIGS. 1 and 3, as well as by two sidefaces 39, 40, wherein only one of the side faces extending parallel tothe plane of the drawing is visible in FIGS. 1 and 3, namely the sideface 39. The top face 37 and the bottom face 38 extend toward each otherin the direction 43 of the medium flowing in the measurement conduit 30toward the measurement element 21, and end with a narrowest crosssection at a narrowest point 36 at the outlet 33 of the measurementconduit 30, which at the same time represents an inlet 34 of thedeflection conduit 31. The measurement element 21 with the resistivefilms has a surface 24 exposed to the flow 43 in the measurement conduit30, which is flush with a surface 25 of the mount 23. The faces 37, 38of the measurement conduit 30 extend in planes which and lateral to, oressentially perpendicular to the surface 24 of the plate-shapedmeasurement element 21, and by means of their extending toward eachother as mentioned above enclose an inclination angle α, which ispreferably approx. 8°.

As shown in more detail in FIG. 2, a sectional depiction along a lineII—II in FIG. 1, the two side faces 39 and 40 extend approximatelyparallel to the surface 24 of the measurement element 21. Consequently,an axial tapering of the measurement conduit 30 in the flow direction 43is produced only by means of the faces 37, 38 that approach each other,wherein the measurement element 21 is preferably disposed slightlyupstream of the narrowest point 36 of the measurement conduit 30. Thetapering of the measurement conduit 30 provided in the flow direction 43or the constant reduction of the flow cross section from the inlet 32 tothe outlet 33 has the effect that an accelerated flow is produced in thevicinity of the measurement element 21, which produces avirtually;uninterrupted, uniform parallel flow in the vicinity of themeasurement element 21.

The inclined embodiment of the faces 37, 38 according to the invention,which extends perpendicular to the surface 24 of the measurement element21, as shown in FIG. 2, produces a base part 45 that contains the sideface 39 and the faces 37, 38 and a cover part 46 that is connected tothe base part 45, for example in a detachable manner, wherein thethickness of the wall of the base part 45 is constant in the vicinity ofthe side face 39 and the thickness of the wall of the cover part 46 isconstant in the vicinity of the side face 40. With the providedmanufacture of the base part 45 and the cover part 46 by means ofplastic injection molding, in addition to the simpler manufacture withthe injection molding, the constant thickness of the walls in thevicinity of the side faces 39, 40 produces the advantage that a uniformcooling speed can be set, which assures the maintenance of a preciseflatness of the faces 39 and 40. As shown in FIG. 1, the base part 45also has, for example, a number of channel-shaped recesses 48, which areprovided at least on the edge region of the measurement part 17 and inwhich the cover part 46 can engage by means of projections in order, forexample, to lock the cover part 46 onto the base part 45 in detentfashion. The shaping of the recesses 48, particularly in the vicinity ofthe tapered measurement conduit 30, permits the embodiment of a uniformwall thickness, which during manufacture leads to a uniform coolingspeed so that hollows or distortions in the faces 37, 38 of themeasurement conduit 30 can likewise be prevented.

A second exemplary embodiment according to the invention is shown inFIG. 3, in which all parts that are the same or have the same functionare depicted with the same reference numerals as in FIGS. 1 and 2. Thedevice 1 shown in FIG. 3 has a deflection conduit 31 that is shaped in aslightly modified fashion in relation to FIG. 1 and whose edge face 50,which extends perpendicular to the plane of the drawing and belongs to afirst part 51 of the deflection conduit 31 directly adjoining themeasurement conduit 30, extends obliquely to the measurement conduitaxis 12. Preferably, an inclination angle β that is enclosed by themeasurement conduit axis 12 and the edge face 50 is approximately 45°.However, it is also possible to embody the edge face 50 with aninclination angle β that lies in a range from approx. 30° to 60°. Theinclined edge face 50 is provided in order for the medium that flowsfrom the outlet 33 of the measurement conduit 30 into the first part 51of the deflection conduit 31 to be diverted along the edge face 50 intoa second part 52, without an abrupt flow increase at a step, as is thecase in the device 1 according to FIGS. 1 and 2.

In addition to a conduit contour that is easier to manufacture, theinclined embodiment of the edge face 50 advantageously also results inthe fact that interferences in the flow coming from the outlet 33 of themeasurement conduit 30, which can occur, for example, in the form ofwhorls or in the form of pressure waves, are reflected against the edgeface 50. This time dependent and location dependent reflection of theinterferences against the edge face 50 can almost completely prevent aninfluence of the electrical signal sent by the measurement element 21due to interferences in the flow so that there is a precise measurementresult of the measurement element 21. Moreover, further downstream ofthe edge face 50, an opening 60 can be provided in the deflectionconduit 31, which, for example in the form of a bore in the base part45, produces a connection of the flow in the deflection conduit 31 tothe external flow in the intake line 9. It is also conceivable toprovide this opening 60 only in the cover part 46. Naturally, there canalso be a number of openings 60, for example in the base part 45 and/orin the cover part 46. By means of the at least one opening 60, theresonance chamber, which is embodied by the deflection conduit 31 and isfor the outgoing pressure waves downstream of the outlet 33 of themeasurement conduit 30, can be influenced in such a way that anattenuation of the pressure waves reflected against the edge face 50occurs by means of a pressure equalization. Through the size of thecross section of the at least one opening 60, the natural frequency ofthe resonance chamber can be tuned to the frequency of the outgoingpressure waves in such a way that there is a further improvement of themeasurement value delivered by the measurement element 21.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. A device for measuring the mass of a flowing medium, in anintake air mass of internal combustion engines, comprising atemperature-dependent measurement element that the flowing mediumcirculates around, said measurement element is disposed in a measurementconduit extending in the device from an inlet to an outlet, saidmeasurement conduit is adjoined by a deflection conduit, wherein themeasurement conduit has two faces (37, 38) which extend transversely tothe measurement element (21), and that faces (37, 38) approach eachother in a direction of the flow in the measurement conduit, themeasurement conduit (30) having two additional faces (39, 40) which aredisposed lateral to a surface(24) of the measurement element (21). 2.The device according to claim 1, in which the flow cross section of themeasurement conduit (30) is generally rectangular and the additionalfaces (39, 40) extend parallel to the surface (24) of the measurementelement (21).
 3. The device according to claim 2, in which aninclination angle α respectively enclosed by the faces (37; 38) thatapproach each other and an axis (12) passing through the center of themeasurement conduit (30) is approximately 8°.
 4. The device according toclaim 1, in which an inclination angle α respectively enclosed by thefaces (37; 38) that approach each other and an axis (12) passing throughthe center of the to measurement conduit (30) is approximately 8°. 5.The device according to claim 1, in which the measurement conduit (30)and the deflection conduit (31) are comprised of two attachable parts, abase part (45) and a cover part (46).
 6. The device according to claim5, in which the thickness of the wall of the base part (45) and thecover part (46) is constant in the vicinity of the additional faces (39,40) which extend parallel to the surface (24) of the measurement element(21).
 7. The device according to claim 5, in which recesses (48) areprovided in the base part (45), at least in the vicinity of themeasurement conduit (30), which produce a constant wall thickness of thefaces (37, 38) of the measurement conduit (30).
 8. The device accordingto claim 1, in which an edge face (50) of a first part (51) of thedeflection conduit (31) is embodied as inclined in relation to an axis(12) passing through the center of the measurement conduit (30).
 9. Thedevice according to claim 8, in which an inclination angle β enclosed bythe edge face (50) and the axis (12) of the measurement conduit (30)lies in the range from approximately 30° to 60°.
 10. The deviceaccording to claim 1, in which at least one opening (60) is provided inthe deflection conduit (31), which produces a connection to the mediumcirculating around the device (1).